Delay line with low reflection attenuation for transit-time tubes

ABSTRACT

A delay line with low reflection attenuation for transit-time tubes, particularly for amplification of millimeter waves, employing a wave-guide having a plurality of successive transverse walls which form line cells, each of which has in addition to a central opening for passage of the electron beam, a coupling slot arranged alternately on opposite sides of the delay line, and provided with a plurality of a cylindrical attenuating bodies which project into the line cells with a penetration depth which varies uniformly along the course of the delay line for providing a reflection-free attenuation, in which such transverse wall are provided with recesses therein in which said attenuating bodies are respectively disposed and mechanically stably retained in operative position therein, such attenuating bodies being disposed diametrically opposite to the corresponding coupling slots and with the longitudinal axis of the cylindrical attenuating bodies and of the delay line being at least approximately parallel to one another.

United States Patent 1 1 Gross Dec. 2, 1975 1 1 DELAY LINE WITH LOW REFLECTION ATTENUATION FOR TRANSIT-TIME [73] Assignee: Siemens Aktiengesellschaft, Berlin & Munich, Germany 22 Filed: Sept. 6, 1974 211 Appl. No.: 503,664

Primary Examiner-Saxfield Chatmon, Jr. Attorney. Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A delay line with low reflection attenuation for transittime tubes, particularly for amplification of millimeter waves, employing a waveguide having a plurality of successive transverse walls which form line cells, each of which hasin addition to a central opening for passage of the electron beam, a coupling slot arranged alternately on opposite sides of the delay line, and provided with a plurality of a cylindrical attenuating bodies which project into the line cells with a penetration depth which varies uniformly along the course of the delay line for providing a reflection-free attenuation, in which such transverse wall are provided with recesses therein in which said attenuating bodies are respectively disposed and mechanically stably retained in operative position therein, such attenuating bodies being disposed diametrically opposite to the corresponding coupling slots and with the longitudinal axis of the cylindrical attenuating bodies and of the delay line being at least approximately parallel to one another.

2 Claims, 2 Drawing Figures DELAY LINE WITH LOW REFLECTION ATTENUATION FOR TRANSIT-TIME TUBES BACKGROUND OF THE INVENTION The invention is directed to a delay line with low re flection attenuation, for transit-time tubes, in particular for the amplification of millimeter waves and utilizing a wave-guide with successive transverse walls which form line cells and, in addition to a central opening for the electron beam, are each provided with a'coupling slot, which slots are arranged alternately on opposite sides of the delay line, and provided with cylindrically shaped attenuating bodies which extend into the respective line cells with a depth of penetration which changes uniformly for providing a reflection-free attenuation in the course of the 'delay line.

Delay lines of this type have become known from German AS 2,134,966 in which the delay line attenuating bodies are disposed in cavity resonators which are specially tuned to frequencies in the region of the cuttoff frequency and which, considered in radial direction, are arranged in a series of interaction cells of the delay line (line cells) on a line parallel to the beam direction.

When the delay line is undivided, the attenuating bodies may project into the line cells by equal distances, whereas in the case of a delay line employing a plurality of amplifier sections which are merely electronically coupled to one another, the depth of penetration preferably decreases with an increasing distance from the adjacent section end (attenuation tapering). In the embodiments of the previously mentioned publication, in a delay line constructed of stacked alternately transversed walls and spacers, attenuating bodies of cylindrical shape are inset into the spacers, in a plane which is at right angles to the plane of symmetry of the delay line. In this case, the cylindrical attenuating bodies are provided with different penetration depths by division into various sized portions along their surface line.

The attenuation arrangement of the described delay line has, in accordance with the tuning of the cavity resonators, a frequency-selective effect and also is favorably direction-dependent with low reflection, but involves a considerable production outlay, the difficulties of which are particularly evident when considering the small dimensions involved in millimeter wave technique. Thus, the cavity resonators which are to be provided with a side opening, independently of a specific dimensioning rule, must always be produced with particular care, must accurately close off the two ends of the attenuating bodies which project into the line cells with the sides of the spacers which are adjacent to the transverse walls, for reasons of heat dissapation, and finally very great, time-consuming precision is required to remove from the attenuating bodies, which for example are only fractions of a millimeter thick, portions of which furthermore are to possess specific size relationships to one another along the surface line of said bodies.

BRIEF SUMMARY OF THE INVENTION It is the object of the invention to provide a delay line for high power transit-time tubes whose low reflection and highly effective attenuation requires merely a low technological outlay. It is proposed in accordance with the invention, for the realization of this objective, to provide in a delay line of the type described, attenuat- LII ing bodies which possess a cylindrical shape, are mechanically and stably secured in additional recesses provided in a transverse wall of the line and arranged diametrically opposite the coupling slots, with the longitudinal axis of the cylindrical attenuating bodies and of the delay line lying at least substantially parallel to one another.

In accordance with the invention cylindrical attenuating bodies are capable of being simply produced, it merely being necessary to cut them off a suitable rod in the particular length desired. The attenuating bodies likewise are mechanically stable and can be readily held in operative position in a recess, or extending completely through openings in the transverse walls. If they are soldered in place, the heat losses which arise in the attenuating bodies are conducted from the reaction chamber by shortheat conducting paths which are not obstructed by a heat barrier.

The shortest heat conducting paths are produced in the particularly critical tapering area as here the attenuating bodies which, in the arrangement proposed by the invention, have a relatively short depth of penetration, act mainly in a current-attenuating fashion (they attenuate the wall currents, tie, the magnetic fields) and thus heat can form practically only in surface areas of the attenuating bodies surrounded by the transverse wall. The attenuating bodies projecting more deeply into the wave-guide cells also act in field attenuating fashion. The longer heat paths which thus occur do not, however, entail any danger of destruction since the high frequency energy which is to be attenuated has already, in a large part, been consumed in the preceding relatively short attenuating bodies.

It is known to insert attenuating bodies in a delay line along the axis through openings in the transverse walls, for example see German AS 1,298,202. Such attenuating bodies, however, are elongated and penetrate several transverse Walls. Attenuation tapering is provided by employing a wedge-shaped tapering of the two ends of the bodies.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like: reference characters indicate like or corresponding parts:

FIG. 1 is a longitudinal sectional view through a delay line constructed in accordance with the invention, illustrating details of the attenuating structure; and

FIG. 2 is a similar sectional view of a second exemplary embodiment of a delay line in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring generally to the drawings and in particular to FIG. 1, in which only those portions of a delay line necessary for an understanding of the invention are illustrated, components not necessary to the understanding of the invention, such as input and output coupling components, being omitted from the drawing.

The portion of the delay line illustrated in FIG. 1 is adapted for use in a travelling wave tube for the amplification of millimeter waves, in which the delay line itself comprises a plurality of line discs 1, 2 which are arranged in a series in the direction of the electron beam and are disposed in a stacked arrangement to form a solid block structure. Each line disc is recessed or indented with such recess in each case other than for the end member 3 forming with the adjacent member a line cell 4 defined by cell-dividing transverse walls 5. Each of the latter is provided with a central electron beam opening 6 and a coupling opening 7, with successive line discs being rotatively displaced with respect to each other by 180, and one pair, in each case, forming one period of the delay line. With such arrangement of line discs, the stacked line has a backwards running fundamental wave in the longest wave transmission whereby it is operated in the first forward running space harmonic i.e. between the 1r and the Zn point.

The traverse wall of each line disc, other than the end disc 3 is provided at the side thereof opposite the coupling opening 7 with a recess 8, which in the embodiment illustrated comprises a bore extending through the transverse wall and which is adapted to receive a cylindrical attenuating body 9. To provide a mechanically stable and good heat conductive mounting, the attenuating body 9' may be soldered to the transverse wall 5 and projects into the respective adjacent line cells 4 at opposite sides of the particular transverse wall. To insure that the attenuation arrangement operates in reflection-free manner, the attenuating bodies are graduated as to their length l and are disposed in staggered relation so that their penetration lengths s s initially uniformly increase along the course of the delay line and then uniformly decrease. The provision of attenuating bodies 9 which individually attenuate two adjacent line cells 4 provides not only a mechanically durable attachment of the attenuating bodies but also possesses the advantage that it is possible to achieve the desired results with a relatively low number of attenuating bodies, and to achieve in each case two different penetration depths merely by a simple staggering of one properly dimensioned attenuating body.

In high power transit-time amplifiers the delay line frequently is divided into different line portions or sections which are separated from one another by socalled severs (isolating section terminations) and which are merely electronically coupled to one another. Here, the amplification factors of the individual line portions are so designed that such portions do not start to oscillate. In these line forms the input coupled I-IF energy is to be absorbed at the section terminations as fully and in as reflection-free a manner as possible.

FIG. 2 illustrates a delay line in accordance with the invention incorporating such a design. It differs from the first embodiment described merely in that it possesses an isolating section termination 10 having an electron beam opening 11 and that the entry paths s s, of the attenuating bodies 9 merely increase but do not subsequently decrease along the course of the delay line. The attenuation arrangement is so dimensioned that the main part of the HF energy which enters from the left side of the figure is in fact converted in the tapering region. The uniform changes in the penetration paths can fulfill different functions which are favorable for a low-reflection attenuation. For example, such penetration can increase linearly with the distance from one end of the delay line. For as uniform as possible a heat loading of the delay line it is also possible to select a dependence in which the amount of heat converted in each individual attenuated line cell is approximately the same.

In a multi-portion delay line, constructed in accordance with the invention, with an internal line crosssection of 4.7 mm, only six attenuating bodies 9 having a thickness of 0.8 mm and a length of up to 3 mm (corresponding to a maximum penetration distance of 1.1 mm) were employed in one portion to achieve a practically reflection-free attenuation. Wave guide cells 4 which were provided with attenuating bodies having the full attenuation length were attenuated by more than 4.5 db.

Possible materials'for the attenuating bodies are, for example, tungsten aluminum oxide for lossy beryllium oxide or boron nitride.

It has been proved that an attenuation arrangement, constructed in accordance with the invention, is also dependent upon frequency and in fact in such manner that its attenuating force increases drastically towards the band edge in the region of the upper cut-off frequency of the operating band. This property ensures that, in particular, the undesired 2w oscillation is prevented, which otherwise can readily be excited when the line voltage increases.

Having thus described my invention it will be obvious that although various minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent granted hereon all such modifications as reasonably, and properly come within the scope of my contribution to the art.

I claim as my invention:

1. A delay line with low reflection attenuation for transit time tubes, particularly for amplification of mi]- liineter waves, comprising a wave-guide having a plurality of successive transverse walls which form line cells, each of which have, in addition to a central openingfor the passage of the electron beam, a coupling slot arranged alternately on opposite sides of the delay line, and a plurality of cylindrical attenuating bodies which project into the line cells with a penetration depth which varies uniformly along the course of the delay line for effecting a reflection-free attenuation, said transverse walls having recesses therein in which said attenutating bodies are respectively disposed in mechanically stable operative positions diametrically opposite to the cooperable coupling slots, the longitudinal axes of the cylindrical attenuating bodies and of the delay line being at least approximately parallel to one another.

2. A delay line according to claim 1, wherein the respective attenuating bodies extend through the transverse wall supporting the same and project into the two adjacent line cells, to form an attenuating body in each such cell. 

1. A delay line with low reflection attenuation for transit time tubes, particularly for amplification of millimeter waves, comprising a wave-guide having a plurality of successive transverse walls which form line cells, each of which have, in addition to a central opening for the passage of the electron beam, a coupling slot arranged alternately on opposite sides of the delay line, and a plurality of cylindrical attenuating bodies which project into the line cells with a penetration depth which varies uniformly along the course of the delay line for effecting a reflection-free attenuation, said transverse walls having recesses therein in which said attenutating bodies are respectively disposed in mechanically stable operative positions diametrically opposite to the cooperable coupling slots, the longitudinal axes of the cylindrical attenuating bodies and of the delay line being at least approximately parallel to one another.
 2. A delay line according to claim 1, wherein the respective attenuating bodies extend through the transverse wall supporting the same and project into the two adjacent line cells, to form an attenuating body in each such cell. 